The invention relates to an elastic bearing for a drive assembly of a motor vehicle of the type having bearings at the motor and transmission sides for holding the drive assembly with vibration dampening.
In a motor vehicle the drive assembly is excited to strong body vibrations because of the travel surface unevenness. With a view toward minimizing the affect of these vibrations on the travel comfort, it is provided in a known manner to so construct the aggregate bearing system that the different vibration forms are decoupled as far as possible from one another, for example so that the vertical vibrations (bouncing) are separated from the tilting vibrations.
It has been determined that, especially a decoupling of the vertical vibrations results in an easily excitable vibration due to the road surface unevenness and therefore disadvantageously affects the driving comfort.
An object of the invention is to construct an elastic bearing arrangement for a driving assembly of a motor vehicle, which through an advantageous vibration relationship of the driving assembly assures a good driving comfort.
This object is inventively achieved according to the following characteristics;
a. the bearing arrangement at the engine side and the bearing arrangement at the transmission side exhibit different respective spring stiffnesses;
b. these different spring stiffnesses of the bearing arrangement are so coordinated with respect to one another that the vertical movements of the driving assembly are substantially coupled with rotational movement about an assembly cross axis;
c. the bearing arrangements are so disposed and configured that all other possible vibration movement forms are substantially decoupled from the vertical and rotational movements; and
d. during dampening of the assembly vibrations caused by external forces respectively all in or out spring movements of the harder bearing arrangement are retarded by a second higher frequency movement.
The advantage of the invention consists therein that a very quick reduction in the externally excited driving assembly vibrations is achieved through an advantageous relationship of the vibration movements. This vibration movement relationship is achieved essentially through a coupling of the vertical and rotational or tipping movements. This results from an arrangement characterized that:
a. the bearings are arranged approximately at the level of the center of gravity in order that further vibration forms, such as for example rotating vibration of the assembly about other axes are separated as desired,
b. the distance between the bearings at the motor side and the transmission bearing is as great as possible in order to have achieved a higher frequency of the rotational movement or vibration about the assembly cross axes,
c. the bearings at the motor side and the transmission exhibit different stiffness in order that the required frequency relationship of the two vibration forms and the ratio of 1 to 2 is achieved,
d. the softer bearing is controlled to be very strongly damped.
Also for transversely constructed motors the advantages of the invention can be similarly achieved, whereby for this type of motor arrangement respectively only one motor bearing and one transmission bearing are used.